Part 1

Anti-Lock Control - Traction Control (Part 1)

COMPONENT LOCATIONS - SHEET 1 OF 2

NOTE: LHD (left-hand drive) installation shown, RHD (right-hand drive) installation similar

COMPONENT LOCATIONS - SHEET 1 OF 2 (PART 1):

COMPONENT LOCATIONS - SHEET 1 OF 2 (PART 2):

COMPONENT LOCATIONS - SHEET 2 OF 2

NOTE: RHD (right-hand drive) installation shown, LHD (left-hand drive) installation similar

COMPONENT LOCATIONS - SHEET 2 OF 2 (PART 1):

COMPONENT LOCATIONS - SHEET 2 OF 2 (PART 2):

GENERAL
The anti-lock control - traction control system is based on the 4 channel Bosch 8.0 system and provides these brake functions:
^ ARM (active roll mitigation).
^ ABS (anti-lock brake system).
^ CBC (corner brake control).
^ DSC.
^ EBD (electronic brake force distribution).
^ ETC (electronic traction control).
^ EBA (emergency brake assist).
^ EDC (engine drag-torque control).
^ HDC.

The system consists of these components:
^ A DSC switch.
^ An HDC switch.
^ A stoplamp switch.
^ Four wheel speed sensors.
^ A yaw rate and lateral acceleration sensor.
^ A steering angle sensor.
^ Four warning indicators.
^ A HCU (hydraulic control unit) with attached ABS (anti-lock brake system) module.

DSC SWITCH

DSC SWITCH (PART 1):

DSC SWITCH (PART 2):

The DSC switch allows the DSC function to be selected off. Although Land Rover recommend that DSC is selected on for all normal driving conditions, it may be beneficial to de-select DSC, to maximize traction, under these conditions:
^ If the vehicle needs to be rocked out of a hollow or a soft surface.
^ Driving on loose surfaces or with snow chains.
^ Driving in deep sand, snow or mud.
^ On tracks with deep longitudinal ruts.

The DSC switch is a non-latching switch installed in the center switch pack on the instrument panel. Pressing the DSC switch connects an ignition power feed to the ABS (anti-lock brake system) module. With the first press of the DSC switch, the ABS (anti-lock brake system) module disables the DSC functions. When the DSC switch is pressed again, the ABS (anti-lock brake system) module re-enables the DSC functions. The DSC switch must be pressed for a minimum of 0.3 s for the ABS (anti-lock brake system) module to react. The DSC function is re-enabled at the beginning of each ignition cycle.

The status of the DSC switch selection is shown by the DSC warning indicator. The DSC warning indicator is off while DSC is selected on, and continuously illuminated while DSC is selected off.

A DSC switch request to disable DSC is ignored by the ABS (anti-lock brake system) module if the air suspension system has failed, or is in off-road height at speeds above 60 km/h (37.5 mph).

To guard against incorrect operation or a broken switch, if the input from the DSC switch is held high for more than one minute, a failure is stored in the ABS (anti-lock brake system) module.

Even if DSC is deselected, driving maneuvers with extreme yaw or lateral acceleration may trigger DSC activity to assist vehicle stability.

HDC SWITCH

HDC SWITCH (PART 1):

HDC SWITCH (PART 2):

The HDC switch controls the selection of the HDC function.

The HDC switch is a non-latching switch installed on the center console, to the rear of the gear shift lever. Pressing and releasing the HDC switch momentarily connects an ignition power feed to the ABS (anti-lock brake system) module. With the first press and release of the HDC switch, the ABS (anti-lock brake system) module enables operation of the HDC function. When the HDC switch is pressed and released again, the ABS (anti-lock brake system) module disables operation of the HDC function.

To guard against incorrect operation or a broken switch, if the switch is pressed for more than 10 seconds no change of state occurs. If the input from the HDC switch is held high for more than one minute, a failure is stored in the ABS (antilock brake system) module.

STOPLAMP SWITCH
The stoplamp switch is mounted in the brake pedal bracket and operated by the brake pedal. The stoplamp switch is a Hall effect switch with dual status outputs. Both of the outputs are supplied to the ABS (anti-lock brake system) module. One of the outputs is also supplied to the LCM (lighting control module) (to operate the stoplamps) and to the ECM (engine control module).

Power for the stoplamp switch is provided by a feed from the auxiliary contacts of the ignition switch via the CJB (central junction box). The power circuit is completed by a ground connection from the stoplamp switch to a ground header on the body.

When the brake pedal is not pressed, the outputs from the stoplamp switch are low, between 0 and 2 V. When the brake pedal is pressed the outputs are pulled high to between 8 V and battery voltage.

WHEEL SPEED SENSORS

WHEEL SPEED SENSORS (PART 1):

WHEEL SPEED SENSORS (PART 2):

An active wheel speed sensor is installed in each wheel hub to provide the ABS (anti-lock brake system) module with a rotational speed signal from each road wheel. The head of each wheel speed sensor is positioned close to a 48 tooth sensor ring on the outer diameter of the constant velocity joint of the drive halfshaft. A flying lead connects each sensor to the vehicle wiring.

The wheel speed sensors each have a power supply connection and a signal connection with the ABS (anti-lock brake system) module. When the ignition switch is in position II, the ABS (anti-lock brake system) module supplies power to the wheel speed sensors and monitors the return signals. Any rotation of the drive halfshafts induces current fluctuations in the return signals which are converted into individual wheel speeds and the overall vehicle speed by the ABS (anti-lock brake system) module.

The ABS (anti-lock brake system) module outputs the individual wheel speeds and the vehicle speed on the high speed CAN (controller area network) bus for use by other systems. The quality of the vehicle speed signal is also broadcast on the high speed CAN (controller area network) bus. If all wheel speed signals are available to calculate vehicle speed from, the quality of the vehicle speed signal is set to 'data calculated within specified accuracy.' If one or more wheel speed sensors is faulty, the quality of the vehicle speed signal is set to 'accuracy outside specification'.

The ABS (anti-lock brake system) module monitors the wheel speed sensor circuits for faults. If a fault is detected the ABS (anti-lock brake system) module stores a related fault code and illuminates the appropriate warning indicators, depending on the system functions affected (DSC/ETC, ABS, EBA/EBD, HDC). A warning chime sounds and a related message is shown in the message center.

Since the wheel speed sensors are active devices, a return signal is available when the road wheels are not turning, which enables the ABS (anti-lock brake system) module to check the sensors while the vehicle is stationary. In addition, the direction of travel of each wheel can be sensed. This information is broadcast on the high sped CAN (controller area network) bus for use by other systems.

YAW RATE AND LATERAL ACCELERATION SENSOR

YAW RATE AND LATERAL ACCELERATION SENSOR (PART 1):

YAW RATE AND LATERAL ACCELERATION SENSOR (PART 2):

Located under the center console, the yaw rate and lateral acceleration sensor provides two inputs to the ABS (anti-lock brake system) module, lateral acceleration and yaw rate, for DSC regulation. The sensor is isolated from body/chassis vibrations through its rubber mounting and secured to the transmission tunnel with 2 bolts.

When the ignition switch is in position II, the yaw rate and lateral acceleration sensor receives an ignition power feed from the CJB (central junction box). For yaw rate, the sensor produces a reference signal of 2.5 volts and a linear yaw rate signal from 0.7 to 4.3 volts. For lateral acceleration, the sensor produces a linear signal from 0.5 to 4.5 volts. In addition to using the inputs for DSC regulation, the ABS (anti-lock brake system) module also broadcasts yaw rate and lateral acceleration values, on the high speed CAN (controller area network) bus, for use by other systems.

The ABS (anti-lock brake system) module monitors the yaw rate and lateral acceleration sensor for faults and can be interrogated using T4. If a fault is detected the ABS (anti-lock brake system) module stores a related fault code and sends a CAN (controller area network) signal to the instrument cluster to illuminate the DSC, HDC and brake warning indicators.

The instrument cluster also sounds a warning chime and displays a DSC fault message in the message center.

STEERING ANGLE SENSOR

STEERING ANGLE SENSOR (PART 1):

STEERING ANGLE SENSOR (PART 2):

The steering angle sensor measures the steering wheel angle and the rate of change of the steering wheel angle (known as the steering wheel angle speed). These measurements are output on the high speed CAN (controller area network) bus, together with a quality factor signal, and used by the ABS (anti-lock brake system) module for CBC and DSC operation.

The steering angle sensor is fixed to the pivot bracket of the steering column by three screws. A gear wheel in the steering angle sensor engages with a plastic drive collar fixed onto the lower shaft of the column. Inside the steering angle sensor, the gear wheel meshes with a gear train containing magnets. An eight pin electrical connector provides the interface between the vehicle wiring and integrated circuits in the steering angle sensor.

The steering angle sensor uses the MR (magneto resistive) effect, which evaluates the direction of magnetic fields, to measure the angular position of the lower shaft, and thus the steering wheel angle. When the steering wheel turns, the steering column lower shaft rotates the gear wheel in the steering angle sensor, which drives the gear train and rotates the magnets on the gears. The direction of the magnetic fields is constantly monitored by the steering angle sensor and converted into a steering wheel angle and steering wheel angle speed.

The steering angle sensor performs a plausibility check of the steering wheel angle each time these conditions coexist:
^ The vehicle is traveling in a straight line.
^ The vehicle speed is between 20 and 25 km/h (12.5 and 15.6 mph).
^ The transfer box is in high range.
^ The brake pedal is not pressed.
^ There is no ABS, DSC or ETC activity.

The steering angle sensor uses inputs of wheel speed, yaw rate and lateral acceleration to determine when the vehicle is traveling in a straight line. When all of the conditions co-exist, the steering angle sensor checks the steering angle, which should be 0 ± 15°. If the steering angle is outside the limits on two successive checks, the steering angle sensor changes the quality factor signal to 'outside specification' for the remainder of the ignition cycle and stores a fault code. At the beginning of each ignition cycle the quality factor signal is reset to 'within specified accuracy'.

The status of the steering angle sensor can be determined using T4.

If the steering angle sensor is replaced, the new sensor must be calibrated using T4. The steering angle sensor must also be re-calibrated any time it is disturbed from the steering column, or if the upper and lower steering columns are separated.

Steering Angle Sensor Harness Connector C0862

Steering Angle Sensor Harness Connector C0862:

Steering Angle Sensor Harness Connector C0862 Pin Details

Steering Angle Sensor Harness Connector C0862 Pin Details:

WARNING INDICATORS

Instrument Cluster Warning Indicators

Instrument Cluster Warning Indicators (Part 1):

Instrument Cluster Warning Indicators (Part 2):

ABS (anti-lock brake system) Warning Indicator
The ABS (anti-lock brake system) warning indicator is an amber colored indicator located between the coolant temperature gage and the fuel level gage.

The ABS (anti-lock brake system) warning indicator is continuously illuminated if there is a fault that affects ABS (anti-lock brake system) performance or causes the ABS (anti-lock brake system) function to be disabled.

Operation of the ABS (anti-lock brake system) warning indicator is controlled by a high speed CAN (controller area network) bus message from the ABS (anti-lock brake system) module to the instrument cluster. There is no bulb check of the ABS (anti-lock brake system) warning indicator when the ignition is switched on.

If a fault causes the ABS (anti-lock brake system) warning indicator to be illuminated, the ABS (anti-lock brake system) warning indicator may illuminate after the next engine start, even if the fault has been rectified and cleared from the ABS (anti-lock brake system) module. The ABS (anti-lock brake system) warning indicator will then remain illuminated until vehicle speed reaches 15-20 km/h (9.5-12.5 mph) while additional checks of the related inputs are performed.

Brake Warning Indicator
The brake warning indicator is a dual colored indicator, located in the coolant temperature gage, that illuminates amber for EBA (emergency brake assist) faults and red for EBD (electronic brake force distribution) faults. The brake warning indicator is also used to give warnings of:
^ Low brake fluid level (illuminates red).
^ Brake pad wear (illuminates red).

Operation of the brake warning indicator, for EBA (emergency brake assist) and EBD (electronic brake force distribution) faults, is controlled by high speed CAN (controller area network) bus messages from the ABS (anti-lock brake system) module to the instrument cluster.

When the ignition switch is first turned to position II, the brake warning indicator illuminates amber for approximately 1 second then red for approximately 1 second, as a bulb check.

DSC Warning Indicator
The DSC warning indicator is an amber colored indicator located in the tachometer.

Each time the DSC or the ETC function is active, the DSC warning indicator flashes at 2 Hz. If DSC has been selected off, or there is a fault that disables the DSC or the ETC function, the DSC warning indicator is continuously illuminated. If DSC has been selected off, vehicles also display a message, advising that DSC is switched off.

Operation of the DSC warning indicator is controlled by a high speed CAN (controller area network) bus message from the ABS (anti-lock brake system) module to the instrument cluster.

When the ignition switch is first turned to position II, the DSC warning indicator illuminates for approximately 2 seconds as a bulb check. If a fault during the previous ignition cycle caused the DSC warning indicator to be illuminated, the DSC warning indicator may remain illuminated after the next bulb check, even if the fault has been rectified and cleared from the ABS (anti-lock brake system) module; the DSC warning indicator may remain illuminated during vehicle operation while additional checks of the related inputs are performed.

HDC Information Indicator
The HDC information indicator is a green colored indicator located in the tachometer.

The HDC information indicator is continuously illuminated while the HDC function is selected on and the vehicle is within the parameters for HDC operation; when the vehicle is outside the parameters for HDC operation, the HDC information indicator is flashed at 2 Hz.

Operation of the HDC information indicator is controlled by a high speed CAN (controller area network) bus message from the ABS (anti-lock brake system) module to the instrument cluster.

When the ignition switch is first turned to position II, the HDC information indicator illuminates for approximately 2 seconds, as a bulb check.

HCU
The HCU (hydraulic control unit) is a 4 channel unit that modulates the supply of hydraulic pressure to the brakes under the control of the ABS (anti-lock brake system) module.

The HCU (hydraulic control unit) is installed in the engine compartment, on three mounting bushes attached to the driver side inner fender. Hydraulic pipes connect the HCU (hydraulic control unit) to the master cylinder and the brakes.

The primary and secondary outlets of the master cylinder are connected to primary and secondary circuits within the HCU (hydraulic control unit). The primary circuit in the HCU (hydraulic control unit) has separate outlet ports to the front brakes. The secondary circuit in the HCU (hydraulic control unit) has separate outlet ports to the rear brakes. Each of the circuits in the HCU (hydraulic control unit) contain these components to control the supply of hydraulic pressure to the brakes:
^ A normally open, solenoid operated, pilot valve, to enable active braking.
^ A normally closed, solenoid operated, priming valve, to connect the brake fluid reservoir to the return pump during active braking.
^ A return pump, to generate hydraulic pressure for active braking and return brake fluid to the reservoir.
^ Normally open, solenoid operated, inlet valves and normally closed, solenoid operated, outlet valves, to modulate the hydraulic pressure in the individual brakes.
^ An accumulator and a relief valve, to allow the fast release of pressure from the brakes.
^ Filters, to protect the components from contamination.

The primary circuit also incorporates a pressure sensor to provide the ABS (anti-lock brake system) module with a hydraulic pressure signal.

Contact pins on the HCU (hydraulic control unit) mate with contacts on the ABS (anti-lock brake system) module to provide the electrical connections from the ABS (anti-lock brake system) module to the return pump motor and the pressure sensor. The solenoids that operate the valves are installed in the ABS (anti-lock brake system) module.

Replacement HCU (hydraulic control unit) are supplied pre-filled. After installation on the vehicle, T4 must be used to operate the solenoid valves and the return pump to ensure correct bleeding of the HCU (hydraulic control unit) and brake circuits.

Schematic of HCU (hydraulic control unit)

Schematic of HCU (hydraulic control unit) (Part 1):

Schematic of HCU (hydraulic control unit) (Part 2):

The HCU (hydraulic control unit) has three operating modes: Normal braking/EBD (electronic brake force distribution), ABS (anti-lock brake system) braking and active braking.

Normal Braking/EBD Mode
Initially, all of the solenoid operated valves are de-energized. Operating the brake pedal produces a corresponding increase or decrease of pressure in the brakes, through the open pilot valves and inlet valves. If the ABS (anti-lock brake system) module determines that EBD (electronic brake force distribution) is necessary, it energizes the inlet valves for the brakes of the trailing axle, to isolate the brakes from any further increase in hydraulic pressure.

ABS Braking Mode
If the ABS (anti-lock brake system) module determines that ABS (anti-lock brake system) braking is necessary, it energizes the inlet and outlet valves of the related brake and starts the return pump. The inlet valve closes to isolate the brake from pressurized fluid; the outlet valve opens to release pressure from the brake into the accumulator and the return pump circuit; the reduced pressure allows the wheel to accelerate. The ABS (anti-lock brake system) module then operates the inlet and outlet valves to modulate the pressure in the brake to apply the maximum braking effort without locking the wheel. Control of the valves for each wheel takes place individually.

Active Braking Mode
The active braking mode is used to generate and control hydraulic pressure to the brakes for functions other than ABS (anti-lock brake system) braking, e.g. DSC, EBA, ETC, HDC and dynamic application of the parking brake.

For active braking, the ABS (anti-lock brake system) module energizes the pilot valves and priming valves, starts the return pump and energizes all of the inlet valves. Brake fluid, drawn from the reservoir through the master cylinder and priming valve, is pressurized by the return pump and supplied to the inlet valves. The ABS (anti-lock brake system) module then operates the inlet valves and outlet valves, as required, to modulate the pressure in the individual brakes. Some noise may be generated during active braking.